Energy systems, such as energy storage systems and/or solar power generation systems have become increasingly used to deliver power to utility grids either as part of standalone energy storage systems or as part of a renewable energy farm (e.g. a wind farm or solar farm). For instance, energy storage systems can include one or more battery banks or other energy storage devices that can be coupled to an AC power system (e.g. electrical grid) via a suitable power converter. Energy storage systems have the ability to both deliver and reserve energy for particular grid services.
A typical energy system (e.g. energy storage system, solar power generation system, etc.) includes a two-winding transformer having a medium voltage primary (e.g. 6 KVAC, 12 KVAC, etc.) and a low voltage secondary (e.g. 575 VAC, 690 VAC, etc.) to couple the energy system to the electrical grid. As used herein, the term “low voltage” can refer to voltages less than or equal to 1.5 kV, and the term “medium voltage” can refer to voltages greater than 1.5 kV and less than 100 kV. For instance, FIG. 1 depicts an example energy storage system 250 having such two-winding transformer 252. As shown, a medium voltage primary winding 254 of the transformer 252 can be coupled to the medium voltage AC power system. A line bus 256 can provide AC power to and from a power converter 262 that can be coupled to a low voltage secondary winding 264 of the transformer 252 either directly or via one or more breakers, fuses, switches, etc. (e.g. breaker 260). In the system 250, the output power of a battery bank 258 and the output power of the power converter 262 can be used to charge or discharge the battery bank 258 depending on the direction of power flow to or from the AC power system. The output power of the power converter 262 and the output power of the battery bank 258 can be operated at the same or similar voltage. For instance, the output power of the power converter 262 and the output power of the battery bank 258 can both be operated at low voltage levels.
Such transformers can be used to increase the low voltage provided by the power converter via the line bus to a medium voltage suitable for output to the AC power system. However, the transformers can be costly and can have a considerable effect on the overall size of the energy system.